Over the last years, the need for very different apparatuses with speech recognition has been dramatically increased; mobile telephone sets installed inside cars are a typical example of the increased need.
Recognition is based upon the extraction of a number of time variable parameters--among which the pitch--from the speech acoustic signal.
The overall reliability of the system hence depends on the reliability with which such parameters are estimated.
Several efforts are being made to obtain the optimal method of estimating the pitch, but at the present time a quite satisfactory method has not been found yet.
One category of such methods is called PAD (Peak Amplitude Detector) and is based on time scanning of the speech acoustic signal in search of a pair of peaks which comply with given characteristics; the time distance between the two peaks corresponds to the searched pitch.
As none of the known algorithms is fully satisfactory, each for several reasons: such as because it requires complicated and requires long calculations and, consequently, it is either not suitable for use in real time or requires very complicated and expensive calculation systems, because it is necessary to consider the speech signal for long times, because, in case of an error in estimate, such error drags itself on the following estimates, and so on.